The present invention relates to pumps in general, and in particular to an improved, reciprocating, air operated pump for fluids.
Compressed air operated pumps find use where relatively inexpensive, low volume pumps are required, or in situations where electric power for the motors of conventional electrically operated pumps is not available. As such pumps depend upon an external supply of compressed air for their power, they generally do not include the bulk and expense of pumps having integral power sources.
Air operated pumps ordinarily include an air cylinder or the equivalent as an air motor for operating a fluid pumping portion of the pump, and a shift valve is often used as a means for selectively applying compressed air to inlets to the cylinder to reciprocatingly move the cylinder to operate the pumping portion. The shift valve is usually mechanically linked directly with the cylinder for operation thereby, whereby at opposite ends of the cylinder travel the valve switches the application of air alternately between the inlets to provide for reciprocating movement of the cylinder. Unfortunately, since the valve is constrained to movement with the cylinder, with conventional pumps there is ordinarily a relatively long period of time, as the cylinder approaches opposite ends of its travel, when the shift valve, in switching from a connection with one inlet to another, does not apply compressed air through any inlet. This results in a decrease in the capacity of the pump and in the efficiency of operation thereof.